The present disclosure relates to a surface-mount device (SMD) inductor, and more particularly, to an inductor used in a high frequency band of 100 MHz or more.
A surface-mount device (SMD) inductor component is generally mounted on a circuit board. Such a product, used at a high frequency of 100 MHz or more, is referred to as a high-frequency inductor.
A high-frequency inductor is mainly used in an LC circuit for impedance matching. For example, multi-band devices that are configured for wireless communications at various frequencies may include such impedance matching circuits and, with the growth of the market for multi-band devices, the number of matching circuits in use is significantly increased. As a result, demand for high-frequency inductors has also increased.
An important technical trend in high-frequency inductors is the implementation of high-Q factor devices. Here, Q may be evaluated as wL/R (Q=wL/R). That is, a Q value is a function of a ratio of inductance (L) and resistance (R) in a given frequency band. Due to the trend for miniaturization of electronic components, efforts are being made to increase the Q value of inductors while decreasing sizes of the elements.
As noted above, high-frequency inductors are used in impedance matching circuits, and such high-frequency inductors may be manufactured so as to be suitable for a specific nominal inductance (L). Furthermore, in order to implement high-Q factor components, the components are generally required to be manufactured to have a higher Q value at a constant nominal inductance L.
However, referring to the Equation Q=wL/R, in order to increase Q while maintaining a same inductance, resistance (R) should be decreased in a use frequency band. As such, in a high frequency region of about 100 MHz to about 5 GHz, in which the high-frequency inductor is mainly used, there is a need to decrease resistance.
In order to decrease resistance, the thickness or the line width of a circuit coil pattern can be increased. In a case in which the line width is increased, an area of an internal core through which magnetic flux flows may be decreased and, as a side effect, inductance L may be decreased.
Therefore, it may instead be preferable to decrease resistance by decreasing an interlayer distance between coils while increasing the thickness of the coil pattern.
However, it is technically difficult to increase the thickness of the coil pattern, and since there is a height difference between a portion on which a coil is present and a portion on which the coil is not present in each of the layers to be stacked due to a thickness of the coil, a special method for decreasing the height difference may be required.
According to the related art, a high-frequency inductor is commonly manufactured using multilayer ceramic technology. That is, inductors have been manufactured by preparing a slurry using ferrite or a dielectric powder, a glass ceramic material, to manufacture a sheet; forming a circuit coil pattern using a conductive material formed of a silver (Ag) ingredient and a screen printing method to manufacture each of the layers; simultaneously stacking the manufactured layers; sintering the stacked layers; and then, forming external terminal electrodes thereon.
In a ceramic inductor according to the related art, a circuit coil pattern has been formed by a screen printing method.
As a result, a limit is reached on increasing a thickness of the circuit coil pattern at the time of printing the circuit coil pattern, and the thickness of the wire may decrease during sintering, such that it is difficult to increase the thickness of circuit coil patterns.
In addition, even in a case of increasing the thickness of the circuit coil pattern, at the time of simultaneously stacking each of the layers, a step portion may be generated. However, in the related art using ceramic sheets, a separate process and materials, such as printing of a non-circuit part, a step portion absorption sheet, and the like, are required in order to solve the step portion problem as described above, and this separate process may deteriorate manufacturing yield and productivity.